Condensation polymerization reaction polymers are used in a wide variety of fields of resins that are in high demand as engineering plastics, including polycarbonates and polyamides, and polyester-based resins used in PET bottles. For example, aromatic polycarbonates are engineering plastics with excellent transparency and heat resistance, as well as excellent mechanical strength including impact strength, and they are widely used for industrial purposes including optical disks, electrical and electronic fields, automobiles, and the like. This has led to a worldwide demand exceeding 3 million tons per year, with continuously increasing growth.
Aromatic polycarbonates are industrially produced by interfacial polycondensation methods using aromatic dihydroxy compounds (for example, 2,2-bis(4-hydroxyphenyl)propane (hereunder referred to as “bisphenol A”) and phosgene as starting materials.
On the other hand, methods for producing aromatic polycarbonates from aromatic dihydroxy compounds and diaryl carbonates are also known, and include transesterification methods in which an aromatic dihydroxy compound (for example, bisphenol A) and a diaryl carbonate (for example, diphenyl carbonate) are transesterified in a molten state, and polymerization is carried out while removing out the aromatic monohydroxy compound (for example, phenol) that is produced. Transesterification methods are advantageous in that they do not use solvents, unlike interfacial polycondensation methods, but they are also associated with certain problems. Namely, the transesterification reaction is an equilibrium reaction with a low equilibrium constant, and therefore polymerization does not proceed unless the aromatic monohydroxy compound (for example, phenol) that is produced is efficiently removed from the surface of the molten product. In addition, the polymer viscosity increases abruptly at a certain point in the polymerization process, making it difficult to efficiently remove the aromatic monohydroxy compound by-product (for example, phenol) out of the system, and presenting a fundamental problem that prevents a high polymerization degree from being obtained.
Various types of polymerization reactors have conventionally been known for production of aromatic polycarbonates by transesterification methods. For example, some known methods employ vertical-type stirred-tank polymerization reactors equipped with stirrers. On small scales, such vertical-type stirred-tank polymerization reactors have high volumetric efficiency, are simple and allow efficient polymerization to proceed, but on an industrial scale, vertical-type stirred-tank polymerization reactors can only be used for production of prepolymers with a low polymerization degree. Some methods are known for solving these problems, such as a method using a screw-type polymerization reactor with a vent (Patent document 1), a method using an intermeshing twin-screw extruder (Patent document 2), a method using a thin-film evaporating reactor such as a screw evaporator or a centrifugal-film evaporator (Patent document 3), and a method using a combination of a centrifugal-film evaporator and a horizontal twin-screw stirring polymerization reactor (Patent document 4).
These methods, however, are all based on mechanical stirring technology and are limited in the polymerization degree of the polycarbonate that can be produced, while they are poorly suited for production of high-molecular-weight aromatic polycarbonates that are widely used for sheet purposes, and therefore numerous problems remain to be resolved.
The present inventors have already published our findings that such problems can be completely solved by developing methods using a guide-contact fluidized polymerization apparatus wherein a molten prepolymer is polymerized while dropping by its own weight along a guide such as a wire, without carrying out mechanical stirring (Patent documents 5-14). Such methods are excellent for production of aromatic polycarbonates.